A conventional pressure reducing valve assembly is shown in FIG. 1 (JP Laid-open Publication No. 111525/1978). This pressure reducing valve assembly is provided with a spool which is slidably accommodated in a cylindrical chamber 9 formed inside a housing 1 and is adapted to introduce a fluid pressure at an outlet port B to a pilot chamber 3 formed at one end of a spool 2 by way of a passage 4. The other end of the spool 2 is pressed with the aid of an electromagnetic unit 5, and then the spool 2 is axially moved so that the pressure P.sub.B at the outlet port B or the pressure of the pilot chamber 3 is adapted to be counterbalanced to the operating force caused by the electromagnetic unit 5 and the pressure P.sub.B can be regulated. The fluid medium flows from an inlet port A to the outlet port B, being controlled at a corner 6a on one end of the land 2a of the spool 2. The corner 6a is so designed that the fluid medium may diverge from the core of the spool 2 in the shape of trumpet as shown with an arrow. A fluid medium flows from the pilot chamber 3 communicated to the outlet port B to a return port T, being regulated at a corner 6b on one end of a land 2b of the spool 2. The corner 6b is so designed that the fluid medium may diverge from the core of the spool 2 in the shape of trumpet as shown with an arrow. In this manner, this traditional pressure reducing valve assembly does not allow the occurrence of what is called a convergent flow to cause the spool 2 to become unstable. Thus, the spool 2 Can be stable, and the generation of vibration and noise can be prevented.
However, this conventional pressure reducing valve assembly has an inherent disadvantage as follows: since the pressure P.sub.B at the outlet port B to be introduced into the pilot chamber 3 is adapted to counterbalance with the limited operating force of the electromagnetic unit 5 with the spool 2 interposed therebetween, the pressure P.sub.B can not be regulated high. In other words, it is impossible in a practical use to control the pressure P.sub.B at the outlet port B to be high with the aid of the electromagnetic unit 5, because it is necessary for the electromagnetic unit 5 to increase in size and weight in order to generate a strong pushing force. On the other hand, if the diameter of the spool 2 is made larger to control a large amount of fluid flow, the fluid power applied to the end of the spool 2 on the side of the pilot chamber 3 will be stronger and consequently, the operating force of the electromagnetic unit 5 cannot be counterbalanced to the fluid power. In short, the disadvantage inherent in said conventional pressure reducing valve assembly lies in its unability of regulating the large amount of fluid flow by means of high pressure.
Accordingly, the object of the present invention is to control the fluid pressure to be high and to control a large amount of fluid flow, simultaneously obtaining a stability of a spool due to the divergency of the fluid flow.